1. Field of the Invention
The present invention relates to a waste disposal site, more particularly to a waste disposal site equipped with a water-impermeable material damage-detecting system which is capable of detecting damages to liner or water-impermeable materials employed at the site.
2. Description of Related Art
A waste disposal site is generally formed by digging the ground to a certain appropriate depth, and waste substances are reclaimed in sequence from the bottom of the dug ground. In such a waste disposal site, water-impermeable materials are usually applied to a bottom and a sloped side surface of the disposal site in order to prevent wastewater from diffusing to ambient earth or ground. As a water-impermeable material, synthetic resin sheets or rubber sheets which both have excellent electric-insulating properties are generally used. It should be noted there is a danger that such water-impermeable materials are subject to damages during a construction work of a waste disposal site or during filling of waste substances. There is a further danger that the water-impermeable materials are subject to damages by birds or beasts trespassing on the waste disposal site. Even if such damages are small, they allow waste water in the waste disposal site to leak out, thereby spoil an object of a seepage control. For that reason, a water-impermeable material damage-detecting system is installed to detect occurrence and parts of damage for a quicker treatment such as a repair work.
The water-impermeable material damage-detecting system is an application of an electric exploration technology which, for instance employs bipolar- or tripolar system (see Japanese Patent Publication No. 63901/1994). More particularly, damages to the water-impermeable materials are detected through varied distribution of potential in electric fields formed above and below the water-impermeable materials via electrodes for feed. Specifically speaking, if the water-impermeable materials of electric-insulation properties are damaged under a condition where electric fields are applied above and below the water-impermeable materials, water leakage or the like occurred there will entail electrical current flow, and ambient potential will vary accordingly. The potential variation there is detected via electrodes for measurement disposed in a reticular manner to determine if damage has occurred and to locate the damaged area.
As will be apparent from the above described principles, in a electric water-impermeable material damage-detecting system, electrically-conductive layers covering an entire surface of the water-impermeable materials need to be applied both above and below the water-impermeable materials. Normally, the electrically-conductive layers are provided by the ground of the waste disposal site with respect to below the water-impermeable materials, and are provided by cover soil which covers the water-impermeable materials for protecting water-impermeable materials with respect to above the water-impermeable materials. However, when the sloped side surface must be steep for the purpose of securing site or the like, it is actually difficult to preliminarily apply cover soil to the sloped side surface, so that any electrically-conductive layer or layers cannot be secured before waste are piled thereon. Therefore, an examination for water-impermeable properties required after completion of a waste disposal site cannot be fully conducted with respect to the sloped side surface. Additionally, an examination for water-impermeable properties required during operation of a waste disposal site cannot be fully conducted with respect to the sloped side surface which would still be exposed.
If dual water-impermeable materials are applied, another problem will be raised as to the electrically-conductive layers. When the water-impermeable materials are made dual in structure, it is general to apply cover soil between upper and lower water-impermeable materials to render the cover soil to be an electrically-conductive layer. Therefore, a similar problem to the above as applied to the sloped side surface will be raised. Namely, a steep sloped side surface will make it difficult to apply cover soil to the sloped side surface. Another problem is that cover soil will reduce an effective volume of the waste disposal site. More particularly, cover soil is applied by means of such heavy duty vehicles including a bulldozer, and in order to avoid damages to the water impermeable materials done by the heavy duty vehicles, the cover soil layer needs to have a thickness of approximately 50 to 100 cm. However, such a thickness will reduce the effective volume to a considerable extent. As yet another problem, there is a danger that the electrodes for measurement disposed in a reticular manner may be disordered due to a soil covering work. More particularly, the electrodes for measuring is generally disposed in a reticular manner with an accuracy to a level of centimeters, however such disposition with greater accuracy may be adversely effected by the cover soil to be smoothed by a bulldozer in a soil covering work.